To achieve reliability and redundancy, an enterprise network and its data centers often span multiple physical sites at different geographic locations. These sites may provide similar services and use layer 2 (data link layer) communication within each site. To achieve inter-site dynamic resource allocation and management, virtual machines (VMs) migrate between the sites. For the VM migration to appear transparent to users, the layer 2 networks at the sites are interconnected so the VMs do not change their Internet Protocol (IP) addresses. Virtual private LAN service (VPLS) is a technology for connecting layer 2 networks.
VPLS developed from a proposal for a multi-protocol label switching (MPLS) layer 2 virtual private network (L2VPN). VPLS provides a multi-to-multi point virtual private network (VPN). VPLS offers a robust solution to service providers. With VPLS, the technical advantages of Ethernet technology are combined with the technical advantages of MPLS to emulate all the functionalities of a conventional LAN. VPLS connects geographically isolated Ethernet-based LANs over a service provider's MPLS backbone network so the LANs operate collectively as if they were a single LAN.
Use of the same reference numbers in different figures indicates similar or identical elements.